The lower urinary tract comprises the bladder, urethra, periurethral muscles and sphincters, and accessory organs. The lower urinary tract has two primary functions: the accumulation and storage of urine (continence), and the elimination of urine at an appropriate time (micturition or urination).
In able-bodied individuals, continence is maintained by low-pressure urine storage in a highly compliant bladder, augmented by tonic activity in the internal and external urethral sphincters. Micturition is achieved in such individuals by synergic relaxation of the urethral sphincter and contraction of the bladder.
Supra-sacral spinal cord injury, brainstem stroke, or disease (e.g., multiple sclerosis) can break or otherwise disrupt the path or paths by which electrical signals generated by the brain normally travel to neuromuscular groups in the lower urinary tract and elsewhere in the body. As a result, even though these nerves and muscles are intact, abnormal electrical signals or no electrical signals are received from the spinal cord, and the associated muscles do not function.
In the lower urinary tract, paralysis of the bladder may occur, and, with it, the inability to empty the bladder voluntarily. Loss of bladder control is a major, devastating effect of these conditions.
These conditions can also result in bladder hyper-reflexia, in which the bladder contracts spontaneously at small fluid volumes. Bladder sphincter dysynergia can also occur, in which the external urethral sphincter contracts, rather than relaxes, during bladder contractions. Hyper-reflexia and dysynergia lead to bladder contraction with high pressure, impaired voiding, large post-void residual volumes, and low bladder compliance.
These dysfunctions often lead to ureteric reflux and obstruction, infection of the kidneys, episodes of autonomic dysreflexia with dangerous rises in blood pressure, incontinence that leads to skin problems, frequent urinary tract infections, and long term renal damage. Urological complications are one of the leading causes of morbidity in persons with spinal cord injury. Loss of bladder control also has profound social impact and leads to decreased quality of life. It also leads to large direct medical costs of procedures, supplies, and medications.
Clean self-catheterization, sometimes in combination with anticholinergic agents, is presently the most effective way to treat the neurogenic bladder. This treatment, however, requires individuals with dexterity for catheterization, as well as tolerance for and response to the anticholinergic agents. Even with these individuals, urinary tract infections persist.
Restoration of bladder evacuation and continence has been achieved by electrical stimulation of the sacral nerve roots, coupled with surgical transections of sacral sensory nerve roots (dorsal rhizotomy). The dorsal rhizotomy eliminates bladder hyper-reflexia and bladder-sphincter dysynergia. This technology has resulted in documented medical, quality of life, and financial benefits. However, widespread application of this technology is limited because of the irreversible effects of the dorsal rhizotomy (which leads to loss of reflex erection in males) and the complex surgical implant procedure itself (which requires access through the back along the spine, laminectomies of vertebral bodies, and the risk of cerebrospinal fluid leaks and intradural infections).
Other, physical conditions also have adverse affects on day-to-day bladder function. For example, a condition called urge incontinence, for which there is sometimes no neurological cause found, results in a hyperactive bladder and a loss of continence. There is also a condition called stress incontinence, which can arise after muscle is stretched in the pelvis during childbirth. Bladder instability or dysfunction are also chronic conditions of many elderly people, especially women.
There is a need for systems and methods that can restore bladder and other urinary tract functions, e.g., micturition and/or continence, in a straightforward manner, without requiring self-catheterization, drug therapy, complicated surgical procedures, or irreversible surgical transections of nerve fibers.